Translation:Wacht niet te lang!
You don't have to include a subject? 'je wacht niet te lang'?
No because this is an imperative. You could say: "Wacht u niet te lang!" to be formal
Given the word order in your sentence wouldn't that be a question?
No, that's also the imperative form. It's not really used woth the subject (not anymore at least), but it is still correct Dutch. :)